1. Field of the Invention
This invention relates to information retrieval systems that retrieves data from databases. Particularly, this invention relates to the information retrieval system that uses hierarchically-structured indexes for the retrieving to efficiently narrow down retrieval results. This application is based on patent application No. Hei 9-205278 filed in Japan, the content of which is incorporated herein by reference.
2. Description of the Related Art
In general, the conventional information retrieval systems are designed to operate based on retrieval conditions, which are input by users. For example, when the user inputs retrieval conditions in the form of logical expressions, the conventional information retrieval system retrieves through a retrieval object database storing retrieval object data, which should be retrieved by the system. So, the conventional system provides the user with the retrieval object data, which match with the retrieval conditions. In some case, however, a number of retrieval result data becomes extremely large in response to some retrieval condition(s) input by the user. In such a case, it is necessary to narrow down the retrieval result data. In order to do so, a first example of the conventional information retrieval system requires inputting of a new retrieval condition for narrowing down the retrieval result data, which should be newly created and input by the user.
The paper of Japanese Patent Application, Publication No. Hei 4-114277 discloses a second example of the conventional information retrieval system, that is, an information retrieval device which is designed as follows:
Hierarchically-structured indexes are presented for the user. So, the user selects a node of the hierarchically-structured indexes, based on which the system performs retrieving on retrieval object data.
As described above, the first example of the conventional information retrieval system requires creation of the new retrieval condition by the user in order to narrow down the retrieval result data. So, there is a problem that the creation of the new retrieval condition is troublesome for the user. Particularly, a person such as a beginner who is not accustomed to the computer retrieving so much is not skilled in determination of retrieval conditions by which retrieval result data can be narrowed down. For this reason, such a person should add or delete the retrieval conditions by trial and error to narrow down the retrieval result data, which causes great load in working.
In contrast, the second example of the conventional information retrieval system is capable of performing retrieving of data by merely selecting nodes of the hierarchically-structured indexes, which are presented for the user. So, it is possible to reduce load to the user in working. However, there is a trouble in the case where multiple nodes matching with the object data exist in the same hierarchical level. In such a case, the user cannot make determination of the node within the multiple nodes that provide a most efficient way for narrowing down the retrieval result data. So, there is a problem that a number of the retrieval result data should be extremely large with respect to some node that is selected by the user.